High aspect ratio and reduced undercut trench etch process for a semiconductor substrate

ABSTRACT

A hydrofluorocarbon gas is employed as a polymer deposition gas in an anisotropic etch process employing an alternation of an etchant gas and the polymer deposition gas to etch a deep trench in a semiconductor substrate. The hydrofluorocarbon gas can generate a thick carbon-rich and hydrogen-containing polymer on sidewalls of a trench at a thickness on par with the thickness of the polymer on a top surface of the semiconductor substrate. The thick carbon-rich and hydrogen-containing polymer protects sidewalls of a trench, thereby minimizing an undercut below a hard mask without degradation of the overall rate. In some embodiments, an improvement in the overall etch rate can be achieved.

RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 13/281,715filed on Oct. 26, 2011, the entire contents of which are incorporatedherein by reference.

BACKGROUND

The present disclosure relates to semiconductor processing methods, andparticularly to methods for anisotropically etching a high aspect ratiotrench in a semiconductor substrate while minimizing an undercut, andstructures for effecting the same.

High aspect ratio deep silicon etch techniques are a key enablingtechnology for implementing through silicon via structures andthree-dimensional integration of multiple semiconductor substrates.State of the art deep silicon etch utilizes a time modulated etchprocess, which is typically referred to as a “Bosch” process.

The Bosch process employs alternating cycles of etching employing a SF₆gas and polymer deposition employing a passivation gas, which is afluorocarbon gas that does not include hydrogen. The Bosch processprovides a reasonable level of anisotropy required for forming highaspect ratio structures. However, the Bosch process, as known in theart, has several limitations. One of such limitations is control of etchprofile. Specifically, the cyclical nature of the Bosch process resultsin sidewall scalloping and undercutting of the etched structures.

To mitigate sidewall scalloping and undercutting of an etch mask (whichis a hard mask), increased amounts of the passivation gas may beemployed. However, increasing the amount of the passivation gas suppliedinto the process chamber to reduce sidewall scalloping and undercuttingsignificantly reduces the etch rate of the process, thereby severelylimiting the throughput of the process. Undercutting of the hard maskresults in formation of voids in a through substrate via that issubsequently formed by filling the trench with a conductive material. Alarge undercut results in a large void within the through substrate viastructure, and is a reliability concern for a three-dimensionalsemiconductor stack having vertical electrical connections through thethrough substrate via structures.

SUMMARY

A hydrofluorocarbon gas is employed as a polymer deposition gas in ananisotropic etch process employing an alternation of an etchant gas andthe polymer deposition gas to etch a deep trench in a semiconductorsubstrate. The hydrofluorocarbon gas can generate a thick carbon-richand hydrogen-containing polymer on sidewalls of a trench at a thicknesson par with the thickness of the polymer on a top surface of thesemiconductor substrate. The thick carbon-rich and hydrogen-containingpolymer protects sidewalls of a trench, thereby minimizing an undercutbelow a hard mask without degradation of the overall rate. In someembodiments, an improvement in the overall etch rate can be achieved.

According to an aspect of the present disclosure, a method of forming asemiconductor structure is provided, which includes: providing a stackof a semiconductor substrate and a mask layer having an opening therein,wherein a top surface of the semiconductor substrate is physicallyexposed at a bottom of the opening; and repeatedly performing a sequenceof an etch process and a deposition process on the stack. The etchprocess removes a semiconductor material at a bottom surface of a trenchunderlying the opening, and the deposition process deposits ahydrofluorocarbon polymer on the bottom surface and sidewalls of thetrench that is generated from a plasma containing ions of ahydrofluorocarbon gas.

According to another aspect of the present disclosure, a semiconductorstructure is provided, which includes: a stack of a semiconductorsubstrate and a mask layer having an opening therein; a trench locatedwithin the semiconductor substrate and underlying the opening and havinga vertically modulated width; and a hydrofluorocarbon polymer layercontiguously extending from a top surface and sidewalls of the masklayer, through sidewalls of the trench, and to a bottom surface of thetrench. The hydrofluorocarbon polymer layer has a first composition atthe bottom surface of the trench, the hydrofluorocarbon polymer has asecond composition at the sidewalls of the trench, and the secondcomposition is different from the first composition.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1A-1L are sequential schematic vertical cross-sectional views ofan exemplary structure in which a through substrate via structure isformed by filling a deep trench formed by a method according to anembodiment of the present disclosure.

FIG. 2 is a schematic diagram illustrating a flow of an etchant gas anda flow of a deposition gas into a process chamber during a trench etchprocess according to an embodiment of the present disclosure.

FIG. 3 is a schematic vertical cross-sectional view of an exemplary teststructure employed to measure deposition rate of hydrofluorocarbonpolymers deposited during a deposition step of a trench etch processaccording to an embodiment of the present disclosure.

FIG. 4 is a deposition rate, at various locations, of a depositionprocess employing C₅HF₇ gas as a deposition gas as measured on a samplehaving the configuration of the exemplary test structure of FIG. 3according to an embodiment of the present disclosure.

FIG. 5 is a deposition rate, at various locations, of a comparativeexemplary deposition process employing C₄F₈ gas as a deposition gas asmeasured on a sample having a configuration of the exemplary teststructure of FIG. 3 that was generated during research leading to thepresent disclosure.

FIGS. 6A-6C are optical emission spectra of three comparative exemplarydeposition processes that were generated during research leading to thepresent disclosure. FIGS. 6D-6F are optical emission spectra for threedeposition processes according to embodiments of the present disclosure.

FIG. 7 is a graph comparing net etch rates of various comparativeexemplary repetitive alternating sequences of etch processes anddeposition processes, and repetitive alternating sequences of etchprocesses and deposition processes according to various embodiments ofthe present disclosure.

FIG. 8 is a graph comparing undercut dimensions of the variouscomparative exemplary repetitive alternating sequences of etch processesand deposition processes, and the repetitive alternating sequences ofetch processes and deposition processes according to various embodimentsof the present disclosure.

FIG. 9 is a graph illustrating resistance to fluorine exposure of afirst comparative deposition process and a first exemplary depositionprocess according to an embodiment of the present disclosure.

FIG. 10 is a graph illustrating resistance to fluorine exposure of asecond comparative deposition process and a second exemplary depositionprocess according to an embodiment of the present disclosure.

FIG. 11 is a graph illustrating the composition of various polymerdeposits before, and after, treatment with SF₆ plasma as analyzed byX-ray photoemission spectroscopy according to the first and secondcomparative processes and the first and second exemplary depositionprocesses according to embodiments of the present disclosure.

FIG. 12 shows Fourier-transformation infrared spectroscopy spectra froma polymer deposit generated by the first comparative exemplarydeposition process before, and after, treatment with SF₆ plasma.

FIG. 13 shows Fourier-transformation infrared spectroscopy spectra froma polymer deposit generated by the first exemplary deposition processbefore, and after, treatment with SF₆ plasma according to an embodimentof the present disclosure.

FIG. 14 shows Fourier-transformation infrared spectroscopy spectra froma polymer deposit generated by the second comparative exemplarydeposition process before, and after, treatment with SF₆ plasma.

FIG. 15 shows Fourier-transformation infrared spectroscopy spectra froma polymer deposit generated by the second exemplary deposition processbefore, and after, treatment with SF₆ plasma according to an embodimentof the present disclosure.

FIG. 16 is a graph showing normalized absorbance of the polymer depositgenerated by the first comparative exemplary deposition process before,and after, treatment with SF₆ plasma.

FIG. 17 is a graph showing normalized absorbance of the polymer depositgenerated by the first exemplary deposition process before, and after,treatment with SF₆ plasma according to an embodiment of the presentdisclosure.

FIG. 18 is a graph showing normalized absorbance of the polymer depositgenerated by the second comparative exemplary deposition process before,and after, treatment with SF₆ plasma.

FIG. 19 is a graph showing normalized absorbance of the polymer depositgenerated by the second exemplary deposition process before, and after,treatment with SF₆ plasma according to an embodiment of the presentdisclosure.

DETAILED DESCRIPTION

As stated above, the present disclosure relates to methods foranisotropically etching a high aspect ratio trench in a semiconductorsubstrate while minimizing an undercut, and structures for effecting thesame, which are now described in detail with accompanying figures.Throughout the drawings, the same reference numerals or letters are usedto designate like or equivalent elements. The drawings are notnecessarily drawn to scale.

Referring to FIG. 1A, an exemplary structure according to an embodimentof the present disclosure includes a semiconductor substrate 10 thatincludes a semiconductor material. The semiconductor material can be anelemental semiconductor material, a III-V compound semiconductormaterial, a II-VI compound semiconductor material, or a combinationthereof. In one embodiment, the semiconductor material can be asilicon-containing material. For example, the semiconductor material ofthe semiconductor substrate 10 can include silicon, a silicon-germaniumalloy, a silicon-carbon alloy, or a silicon-germanium-carbon alloy. Inone embodiment, the semiconductor material can be silicon. Thesemiconductor material of the semiconductor substrate 10 can be undopedor doped with electrical dopants such as B, Ga, In, P, As, and/or Sb.Semiconductor devices (not shown) and/or metal interconnect structures(not shown) can be included in the upper portion of the semiconductorsubstrate. The thickness of the semiconductor substrate 10 can be from30 microns to 2 mm, although lesser and greater thicknesses can also beemployed.

A mask layer 20 is formed on the top surface of the semiconductorsubstrate 10, and is patterned to form openings therein. It isunderstood that a plurality of openings can be formed in the mask layer20 although a single opening is illustrated in FIGS. 1A-1L. The masklayer 20 can be a hard mask layer including a dielectric material or ametallic material. Dielectric materials that can be employed for themask layer 20 include, but are not limited to a dielectric materialselected from doped silicon oxide, undoped silicon oxide, siliconnitride, silicon oxynitride, a dielectric metal oxide, and a combinationthereof. Metallic materials that can be employed for the mask layer 20include, but are not limited to, TiN, TaN, WN, WC, TiC, TaC, W, Ti, Ta,Cu, Al, and combinations or alloys thereof. The mask layer 20 can bepatterned, for example, by applying a photoresist (not shown) thereupon,patterning the photoresist by lithographic exposure and development, andtransferring the pattern in the photoresist into the mask layer 20employing an etch, which can be an anisotropic etch such as a reactiveion etch or an isotropic etch such as a wet etch. Alternatively, themask layer 20 can include an organic material such as a patternedphotoresist material or a patterned layer of an optically planarizingmaterial as known in the art. The thickness of the mask layer 20 can befrom 0.2 microns to 10 microns, although lesser and greater thicknessescan also be employed.

The width w of an opening in the mask layer 20 can be from 1 micron to70 microns, although lesser and greater widths w can also be employed.The opening can have a shape of a circle, an ellipse, or rectangle inwhich the lesser distance between two pairs of sides corresponds to thewidth w.

Referring to FIG. 1B, the exemplary structure is placed in a processchamber configured to generate a plasma therein. The process chamber canbe, for example, a reactive ion etch chamber configured to generate aplasma by coupling radio frequency (RF) electromagnetic field to the agas therein.

For example, the process chamber can be a vacuum chamber including alower electrode on which the exemplary structure is mounted, and anupper electrode vertically spaced from the exemplary structure by aspacing. The power coupled to the plasma through the RF electromagneticfield is herein referred to as a plasma power. In addition, a constantvoltage bias can be applied between the lower electrode and the upperelectrode to induce the ions in the plasma to impinge on the substratein contact with the lower electrode. The power coupled to the plasmathrough the constant voltage bias is herein referred to as a bias power.The oscillating electric field ionizes the gas molecules by strippingelectrons from the gas molecules, thereby creating a plasma.

Once the exemplary structure is loaded into the process chamber suchthat the bottom surface of the semiconductor substrate 10 contacts thelower electrode, and the upper electrode is more proximal to the masklayer 20 than to the bottom surface of the semiconductor substrate 10,an etchant gas is flowed into the process chamber, for example,employing a mass flow controller. A non-limiting example of the etchantgas is sulfur hexafluoride (SF₆). Other etchant gases known in the artsuch as, for example, CF₄, CHF₃, Cl₂, HBr, and/or combinations thereofcan also be employed to remove the semiconductor material of thesemiconductor substrate 10.

An etch process is performed by generating a plasma of the etchant gas.The plasma of the etchant gas can be generated in the process chamber byapplying a bias voltage and an RF electromagnetic field, and therebycoupling the plasma power and the bias power to the etchant gas. Theetchant gas is ionized to form a plasma containing etchant ions. Theetchant ions are accelerated toward the exemplary structure to etch thesemiconductor material of the semiconductor substrate 10. Because ofstatistical distribution of velocity of the radicals in the plasma andthe associated efficacy for forming volatile adsorbates, a lateral etchaccompanies a vertical etch of the semiconductor material in thesemiconductor substrate 10. Thus, a trench 11 formed underneath eachopening in the mask layer includes a peripheral undercut region. Theundercut region of the trench 11 is the portion of the trench 11 thatdoes not overlap the area of an overlying opening in the mask layer 20in a top-down view in a direction perpendicular to the interface betweenthe semiconductor substrate 10 and the mask layer 20. The undercutregion is formed directly underneath portions of the mask layer 20around the corresponding opening in the mask layer 20.

The pressure of the plasma of the etchant ions can be from 1 mTorr to 30mTorr, although lesser and greater pressures can also be employed. Theetch rate of the semiconductor material during the etch process can befrom 1 micron per minute to 10 microns per minute, although lesser andgreater etch rates can also be achieved. The temperature of the etchprocess can be from −30 degrees Centigrade to 60 degrees Centigrade,although lesser and greater temperatures can also be employed. The timeduration of the etch process can be from 1 second to 1 minute, althoughlesser and greater time durations can also be employed.

Referring to FIG. 1C, after the etch process is performed for a timeperiod, a deposition process is performed in the same process chamber.Specifically, the etchant gas in the process chamber is pumped out ofthe process chamber, and a deposition gas is flowed into the processchamber, for example, employing a mass flow controller. The depositiongas includes a hydrofluorocarbon gas having a chemical formula ofC_(x)H_(y)F_(z), wherein x is an integer selected from 3, 4, 5, 6, and7, y and z are positive integers not greater than 15. Hydrofluorocarbongas having a chemical formula of C_(x)H_(y)F_(z), wherein x is aninteger selected from 4, 5, 6, and 7, y and z are positive integers notgreater than 15 is preferable. Hydrofluorocarbon gas having unsaturatedbond such as double bond, triple bond and cyclic structure ispreferable. It is preferable that a ratio of fluorine atom to carbonatom of hydrofluorocarbon is greater than 0.6 and not greater than 2.0.For example the hydrofluorocarbon gas can include [C3]1,1-difluoropropene, 1,2-difluoropropene, 1,3-difluoropropene,2,3-difluoropropene, 3,3-difluoropropene, 1,1-difluorocycropropane,1,2-difluorocycropropane, 1,1,2-trifluoropropene,1,1,3-trifluoropropene, 1,2,3-trifluoropropene, 1,3,3-trifluoropropene,2,3,3-trifluoropropene, 3,3,3-trifluoropropene,1,1,2-trifluorocycropropane, 1,2,3-trifluorocycropropane,1,1,2,3-tetrafluoropropene, 1,1,3,3-tetrafluoropropene,1,2,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene,2,3,3,3-tetrafluoropropene, 1,1,2,2-tetrafluorocycropropane,1,1,2,3-tetrafluorocycropropane, 1,3-difluoropropyne,3,3-difluoropropyne, 1,2-difluoropropadiene, 1,3-difluoropropadiene,1,3,3-trifluoropropyne, 3,3,3-trifluoropropyne,1,1,3-trifluoropropadiene, [C4] 3,3,4,4-tetrafluorocycrobutene,1,3,3,4,4-pentafluorocycrobutene, 1,1,2,2,3,4-hexafluorocycrobutane,1,1,2,2,3-pentafluorocycrobutane, 1,1,2,2,3,3,4-heptafluorocycrobutane,1,1,1,4,4,4-hexafluoro-2-butene,3,3,3-trifluoro-2-trifluoromethylpropene,1,1,2,3,4-pentafluoro-1,3-butadiene,1,1,2,4,4-pentafluoro-1,3-butadiene, 1,1,2,3-tetrafluoro-1,3-butadiene,1,1,2,4-tetrafluoro-1,3-butadiene, 1,1,3,4-tetrafluoro-1,3-butadiene,1,2,3,4-tetrafluoro-1,3-butadiene, 1,1,4,4-tetrafluoro-1,3-butadiene,1,1,2-trifluoro-1,3-butadiene, 1,1,3-trifluoro-1,3-butadiene,1,1,4-trifluoro-1,3-butadiene, 1,2,3-trifluoro-1,3-butadiene,1,2,4-trifluoro-1,3-butadiene, 1,1,2,3-tetrafluoro-1-butene,1,1,2,4-tetrafluoro-1-butene, 1,1,3,3-tetrafluoro-1-butene,1,1,3,4-tetrafluoro-1-butene, 1,1,4,4-tetrafluoro-1-butene,1,2,3,3-tetrafluoro-1-butene, 1,2,3,4-tetrafluoro-1-butene,1,2,4,4-tetrafluoro-1-butene, 1,3,3,4-tetrafluoro-1-butene,1,3,4,4-tetrafluoro-1-butene, 1,4,4,4-tetrafluoro-1-butene,2,3,3,4-tetrafluoro-1-butene, 2,3,4,4-tetrafluoro-1-butene,2,4,4,4-tetrafluoro-1-butene, 3,3,4,4-tetrafluoro-1-butene,3,4,4,4-tetrafluoro-1-butene, 1,1,1,2-tetrafluoro-2-butene,1,1,1,3-tetrafluoro-2-butene, 1,1,1,4-tetrafluoro-2-butene,1,1,2,3-tetrafluoro-2-butene, 1,1,2,4-tetrafluoro-2-butene,1,1,3,4-tetrafluoro-2-butene, 1,1,4,4-tetrafluoro-2-butene,1,2,3,4-tetrafluoro-2-butene, 1,1,3,3-tetrafluoro-2-methylpropane,1,1,3-trifluoro-2-fluoromethylpropane,1,3,3-trifluoro-2-fluoromethylpropane,3,3-difluoro-2-difluoromethylpropane, 1,1,2,2-tetrafluorocycrobutane,1,1,2,3-tetrafluorocycrobutane, 1,1,3,3-tetrafluorocycrobutane,1,2,3,4-tetrafluorocycrobutane, 1-fluoro-1-trifluoromethylcycropropane,2-fluoro-1-trifluoromethylcycropropane,1,1-difluoro-1-difluoromethylcycropropane,1,2-difluoro-1-difluoromethylcycropropane,2,2-difluoro-1-difluoromethylcycropropane,2,3-difluoro-1-difluoromethylcycropropane,1,2,2-trifluoro-1-fluoromethylcycropropane,1,2,3-trifluoro-1-fluoromethylcycropropane,2,2,3-trifluoro-1-fluoromethylcycropropane,1,2,2,3-tetrafluoro-1-methylcycropropane,2,2,3,3-tetrafluoro-1-methylcycropropane, [C5]1,3,3,4,4,5,5-heptafluorocycropentene,3,3,4,4,5,5-hexafluorocycropentene, 1,1,2,2,5,5-hexafluorocycropentane,1,1,1,3,4,4,5,5,5-nonafluoro-2-pentene,1,1,1,2,4,4,5,5,5-nonafluoro-2-pentene,2,3,4,5,5,5-hexafluoro-1,3-pentadiene,1,3,4,5,5,5-hexafluoro-1,3-pentadiene,1,2,4,5,5,5-hexafluoro-1,3-pentadiene,1,2,3,5,5,5-hexafluoro-1,3-pentadiene,1,2,3,4,5,5-hexafluoro-1,3-pentadiene,1,2,4,5,5,5-hexafluoro-1,3-pentadiene,1,1,2,3,4,-pentafluoro-1,3-pentadiene,3,4,5,5,5-pentafluoro-1,3-pentadiene,1,2,3,3,4-pentafluoro-1,4-pentadiene,1,1,2,3,3-pentafluoro-1,4-pentadiene,1,3,3,4,4-pentafluoro-2-methylcycrobutene,2-fluoro-1-trifluoromethylcycrobutene,3,3,4,4-tetrafluoro-1-trifluoromethylcycrobutene, [C6]1,3,3,4,4,5,5,6,6-nonafluorocycrohexene,3,3,4,4,5,5,6,6-octafluorocycrohexene,1,1,3,3-tetrafluoro-2-trifluoromethylcycropentane,4,5,5,5-tetrafluoro-3-trifluoromethyl-1,3-pentadiene,1,1,2,4,5,5,5-heptafluoro-3-methyl-1,3-pentadiene,1,2-bis(trifluoromethyl)cycrobutane,1,2-bis(trifluoromethyl)cycrobutene,3,4-bis(trifluoromethyl)cycrobutene,1,1,1-trifluoro-2-trifluoromethyl-3-methyl-2-butene,1,1,1-trifluoro-3-trifluoromethyl-2-methyl-2-butene,1,1,1,-trifluoro-3-trifluoromethyl-2-pentene,4,4,5,5,5-pentafluoro-3-methyl-2-pentene, [7]1,3,3,4,4,5,5,6,6,7,7-undecafluorocycroheptene,3,3,4,4,5,5,6,6,7,7-decafluorocycroheptene,1,3,3,4,4,5,5-heptafluoro-2-ethylcycropentene,3,3,4,4,5,5-hexafluoro-1,2-dimethylcycropentene and1,2-bis(fluoromethyl)cycropentene, but these are non-limiting examplesof specific embodiments of the present disclosure. In one embodiment,the hydrofluorocarbon gas is 1,3,3,4,4,5,5-heptafluorocycropentene asC₅HF₇.

A deposition process is performed by generating a plasma of thedeposition gas. The plasma of the deposition gas can be generated in theprocess chamber by applying a bias voltage and an RF electromagneticfield, and thereby coupling the plasma power and the bias power to thedeposition gas. The deposition gas is ionized to form a plasma ofhydrofluorocarbon ions. The hydrofluorocarbon ions are acceleratedtoward the exemplary structure to deposit a hydrofluorocarbon polymerlayer 30 on the top surface and sidewalls of the mask layer 20, and onthe sidewalls and the bottom surface of the trench 11 within thesemiconductor substrate 10. Because of statistical distribution ofvelocity of the radicals in the plasma, the hydrofluorocarbon polymerlayer 30 is deposited as a contiguous layer that contacts the entiretyof the top surface and sidewalls of the mask layer 20, and the sidewallsand the bottom surface of the trench 11 within the semiconductorsubstrate 10.

Various portions of the hydrofluorocarbon polymer layer 30 can havedifferent compositions and different thicknesses due to differentanisotropy for each species of ions present in the plasma. Further,various portions of the hydrofluorocarbon polymer layer 30 can havedifferent thicknesses. For example, a portion of the hydrofluorocarbonpolymer layer 30 located at a bottom of the trench 11 can have a bottompolymer thickness tp_b, a portion of the hydrofluorocarbon polymer layer30 located at a sidewall of the trench 11 and a sidewall of the masklayer 20 can have a sidewall polymer thickness tp_s, and a portion ofthe hydrofluorocarbon polymer layer 30 located at a top surface of themask layer 20 can have a top polymer thickness tp_t.

The pressure of the plasma can be from 1 mTorr to 30 mTorr, althoughlesser and greater pressures can also be employed. The deposition rateof the hydrofluorocarbon polymer material of the hydrofluorocarbonpolymer layer 30 at various locations can be from 50 nm per minute to500 nm per minute, although lesser and greater deposition rates can alsobe employed. The temperature of the deposition process can be from −30degrees Centigrade to 60 degrees Centigrade, although lesser and greatertemperatures can also be employed. The time duration of the etch processcan be from 0.5 second to 30 seconds, although lesser and greater timedurations can also be employed.

Referring to FIG. 1D, the etch process of FIG. 1B is performed again.The parameters for generating the plasma of the etchant radicals andions are selected such that the etchant ions impinge on the exemplarystructure are aligned predominantly along a surface normal of theinterface between the semiconductor substrate 10 and the mask layer 20.The hydrofluorocarbon polymer layer 30 is etched anisotropically suchthat horizontal portions of the hydrofluorocarbon polymer layer 30located at a bottom surface of the trench 11 and on the top surface ofthe mask layer 20 are etched, while portions of the hydrofluorocarbonpolymer layer 30 located on the sidewalls of the mask layer 20 and thesidewalls of the trench 11 are not removed. The species of the etchantgas and the other parameters for generating the plasma of the etchantradicals and ions can be the same as in the etch process of FIG. 1B. Inone embodiment, etch process employs a plasma of a fluorine-containingetchant such as SF₆, and substitutes a fraction of hydrogen atoms in thehydrofluorocarbon polymer material in the hydrofluorocarbon polymerlayer 30 with fluorine atoms prior to removing a fluorine-enhancedhydrofluorocarbon material.

Referring to FIG. 1E, the time duration of the etch process that isinitiated at the step of FIG. 1D is selected such that the etch processcontinues after a bottom portion of the hydrofluorocarbon polymer layer30 is removed and a semiconductor surface is physically exposed at thebottom of the trench 30. The etchant plasma commences etching of thesemiconductor material of the semiconductor substrate 10 such that avertical etch and a lateral etch of the semiconductor material occursimultaneously, while a remaining portion of the hydrofluorocarbonpolymer layer 30 at the sidewalls of the trench 11 protect thesemiconductor material around the remaining portion of thehydrofluorocarbon polymer layer 30. The trench 11 is extended downwardto add a newly added cavity volume. The lateral extent of the newlyadded cavity volume modulates vertically such that the lateral extentincreases gradually and then gradually decreases as a function of depthfrom the level of the bottom surface of the trench 11 at the end of theprocessing step of FIG. 1D. The time duration of this etch process canbe selected such that the hydrofluorocarbon polymer layer 30 iscompletely removed, or only minimally present, at the end of this etchprocess.

Referring to FIG. 1F, once the etch process of FIGS. 1D and 1E iscompleted, the deposition process of FIG. 1C can be repeated to depositthe same type of a hydrofluorocarbon polymer material, and to formanother hydrofluorocarbon polymer layer 30. The process parameters ofthis deposition step can be substantially the same as the processparameters of the step of FIG. 1C.

In general, a sequence of the etch process described above and thedeposition process described above is repeated on the stack of thesemiconductor substrate 10 and the mask layer 20 including openings.Each etch process removes a semiconductor material at a bottom surfaceof the trench 11 underlying an opening, and the deposition processdeposits a hydrofluorocarbon polymer layer 30 on the bottom surface andsidewalls of the trench 11 as well as the top surface and the sidewallsof the mask layer 20. The hydrofluorocarbon polymer material of thehydrofluorocarbon polymer layer 30 is generated from a plasma containingions of the hydrofluorocarbon gas.

At the end of each deposition step, a hydrofluorocarbon polymer layer 30is contiguously deposited on the top surface and sidewalls of the masklayer 20 and on the sidewalls and the bottom surface of the trench 11within the semiconductor substrate 10. The hydrofluorocarbon polymerlayer 30 includes a first hydrofluorocarbon polymer portion 30Adeposited on the bottom surface of the trench 11 and having a firstcomposition and a first thickness, a second hydrofluorocarbon polymerportion 30B deposited on the sidewalls of the trench 11 and thesidewalls of the mask layer 20, and a third hydrofluorocarbon polymerportion 30C deposited on the top surface of the mask layer 20 and havinga third composition and a third thickness.

At the end of each deposition step, the exemplary structure is asemiconductor structure including a stack of the semiconductor substrate10 and the mask layer 20 having an opening therein, the trench 11 thatis located within the semiconductor substrate 10 and underlies theopening and has an vertically modulated width, and a hydrofluorocarbonpolymer layer 30 that extends from the top surface and sidewalls of themask layer 20, through sidewalls of the trench 11, and to the bottomsurface of the trench 11. The hydrofluorocarbon polymer layer 30 has afirst composition at the bottom surface of the trench 11, a secondcomposition at the sidewalls of the trench 11, and the secondcomposition is different from the first composition. Specifically, thesecond composition includes more hydrogen than the first composition,and less fluorine than the first composition as will be discussed below.

The repeated performance of the sequence of the etch process and thedeposition process forms modulations in the lateral dimension, i.e., thewidth, within the trench 11 as a function of depth from the interfacebetween the top surface of the semiconductor substrate 11 and the masklayer 20. The total number of repetitions of the sequence of the etchprocess and the deposition process can be from 2 to 1,000, and typicallyfrom 30 to 200, although a greater number of repetitions can also beemployed. Each repetition of the sequence of the etch process and thedeposition extends the trench 11 downward to add a newly added cavityvolume. The lateral extent of the newly added cavity volume modulatesvertically such that the lateral extent increases gradually and thengradually decreases as a function of depth from the level of the bottomsurface of the trench 11 at the end of the processing step of FIG. 1D.The time duration of this etch process can be selected such that thehydrofluorocarbon polymer layer 30 is completely removed, or onlyminimally present, at the end of each etch process.

Referring to FIG. 2, the flow rate of the etchant gas and the depositiongas, i.e., the hydrofluorocarbon gas, into the process chamber isschematically illustrated as a function of time 2. An etchant gas flowrate curve 210 and a deposition gas flow rate curve 220 are illustratedin the graph of FIG. 2. The time duration represented by t_eacorresponds to an etching active time, during which etching of thesemiconductor material of the semiconductor substrate 10 occurs. Thevalue for t_ea can be from 1 second to 1 minute as discussed above,although lesser and greater values can also be employed. The timeduration represented by t_pa corresponds to a passivation active time,during which the deposition of the hydrofluorocarbon polymer materialoccurs, and the bottom surface and the sidewalls of the trench 11 arepassivated by the hydrofluorocarbon polymer material. The value for t_pacan be from 0.5 second to 30 seconds as discussed above, although lesserand greater values can also be employed. The time duration representedby t_eo corresponds to an etch overlap time, during which the etch rateof the semiconductor material is ramped down and the deposition rate forthe hydrofluorocarbon polymer material is ramped up. The ratio of t_eoto t_pa can be from 0 to 0.5. The time duration represented by t_pocorresponds to a passivation overlap time, during which the depositionrate for the hydrofluorocarbon polymer material is ramped down and theetch rate of the semiconductor material in the semiconductor substrate10 is ramped up. The ratio of t_pa to t_ea can be from 0 to 0.5.

In one embodiment, the flow rate of the etchant gas and flow rate of thedeposition gas can be controlled such that the ramp down time period forthe flow rate of the etchant gas overlaps with the ramp up time periodfor the flow rate of the deposition gas, and the ramp up time period forthe flow rate of the etchant gas overlaps with the ramp down time periodfor the flow rate of the deposition gas. In another embodiment, the timeduration for flow of the etchant gas and the time duration for the flowof the deposition gas can be mutually exclusive, i.e., t_eo and t_po canbe zero. The maximum value for the flow rate of the etchant gas and themaximum value for the flow rate of the deposition gas depends on thespecies of the etchant gas and the deposition gas, the size of theprocess chamber, and the pressures of the etchant gas plasma and thedeposition gas plasma. In a non-limiting illustrative example, if sulfurhexafluoride is employed as the etchant gas and the process chamber isof a size that accommodates a 300 mm diameter substrate, the maximumvalue for the flow rate of the etchant gas can be from 10 sccm to 600sccm, and the maximum value for the flow rate of the deposition gas,i.e., the hydrofluorocarbon gas having a chemical formula ofC_(x)H_(y)F_(z), wherein x is an integer selected from 3, 4, 5, 6, and7, y and z are positive integers not greater than 15, can be from 20sccm to 1,000 sccm.

Referring to FIG. 1G, the last the sequence of the etch process and thedeposition process can be followed by another etch process that extendsthe trench 11 downward for the last time. The trench 11 as providedafter the last etch process has a vertically modulating width, which isherein referred to as “scalloping.” One cycle of modulation of the widthof the trench 11 corresponds to an etch process within a sequence. Thetotal number of cycles in the modulation of the width of the trench 11is the same as the sum of the number of repetitions of the sequence ofthe etch process and the number 1, which corresponds to the last etchprocess that is not followed by a deposition process.

The depth d of the trench can be from 20 microns to 200 microns,although lesser and greater depths can also be employed. The lateraldistance between the outermost lateral extent of a sidewall of thetrench 11 and a sidewall of the mask layer 20 that is most proximal tothat sidewall of the trench 11 in a vertical cross-sectional view in awidthwise direction of the trench 11 is herein referred to as an“undercut dimension” u of the trench 11. As used herein, a widthwisedirection of the trench 11 is a direction along which the lateralseparation distance between two opposing sidewalls is minimized. If theshape of the opening in the mask layer 20 is circular, any verticalpassing through a vertical center axis of the trench 11 is a widthwisedirection. If the shape of the opening in the mask layer 20 isrectangular, the widthwise direction is the direction of a shorter pairof sides of the rectangle that defines a periphery of the opening in atop-down view.

In a non-limiting illustrative example, the undercut dimension u of thetrench 11 can be on the order of 300 nm if the width w of the opening isfrom 3 micron to 5 micron and the depth d of the trench is on the orderof 50 microns, and gradually increases to be on the order of 600 nm ifthe width w of the opening is on the order of 50 microns and the depth dof the trench 11 is on the order of 100 microns. The lateral modulationof a sidewall of the trench 11 as seen in a vertical cross-sectionalview in the widthwise direction can be from 5% to 30% of the undercutdimension.

Referring to FIG. 1H, the surfaces of the trench 11 can be cleaned, forexample, by a wet clean. Optionally, the mask layer 20 may, or may not,be removed. A dielectric liner 40 is deposited on the sidewalls of thetrench 11 by a conformal deposition process such as chemical vapordeposition or atomic layer deposition. The dielectric liner 40 includesa dielectric material such as silicon oxide, silicon nitride, siliconoxynitride, a dielectric metal oxide, or a combination thereof. Thethickness of the dielectric liner 40 can be from 50 nm to 1,000 nm,although lesser and greater thicknesses can also be employed.

Referring to FIG. 1I, a conductive material layer 50L can be depositedto fill the trench 11. The conductive material layer 50L can bedeposited, for example, by chemical vapor deposition, electroplating,electroless plating, or a combination thereof. The conductive materiallayer 50L can include a metallic material such as Cu, Al, W, TaN, TiN,WN, or a combination thereof.

Referring to FIG. 1J, the conductive material layer 50L can beplanarized to form a through substrate via structure 50, for example, bychemical mechanical planarization. The dielectric liner 40 and/or themask layer 20 can be employed as a stopping layer for the planarizationprocess.

Referring to FIG. 1K, a bottom portion of the semiconductor substrate 10can be removed, for example, by grinding or chemical mechanicalplanarization to physically expose a bottom portion of the throughsubstrate via structure 50. A surface of the dielectric liner 40 is alsophysically exposed around the bottom surface of the through substratevia structure 50.

Referring to FIG. 1L, the semiconductor substrate 10 can be bonded to asubstrate 60, for example, through a C4 ball 70. The substrate 60 can beanother semiconductor substrate, a transposer, or a packaging substrate.

Referring to FIG. 3, an exemplary test structure is schematicallyillustrated in a vertical cross-sectional view. In the course ofresearch leading to the present disclosure, test structures having thesame configuration as the exemplary test structure were employed tocharacterize the properties of the hydrofluorocarbon polymer materialthat is deposited during the deposition steps among the repetitiveprocessing sequence between the processing step of FIG. 1B and theprocessing step of FIG. 1G.

The exemplary test structure of FIG. 3 can be formed, for example, byforming a mask layer 20 on a semiconductor substrate, patterning anopening in the mask layer, and transferring the pattern of the openinginto an upper portion of the semiconductor substrate 10 to a depth d′ toform a trench 11′ within the semiconductor substrate 10. The depth d′can be from 20 microns to 200 microns. The width of the trench 11′ canbe from 10 microns to 200 microns so that a hydrofluorocarbon polymermaterial at the bottom of the trench 11′ has a sufficiently large areafor analysis in analytical instruments. The trench 11′ can be formedemploying the processing steps of FIGS. 1A-1G. The modulation of thetrench sidewalls and the undercut dimension of the trench 11′ are notshown in FIG. 3 for simplicity.

The exemplary test structure can be placed in a processing chamber, anda deposition process is performed which is the same as one of thedeposition processes among the repetitive processing sequence of FIGS.1B-1G. For example, the deposition process of FIG. 1C or the depositionprocess of FIG. 1F can be performed with modification to the timeduration of the deposition process. The time duration of the depositionprocess for forming the exemplary test structure illustrated in FIG. 3is selected such that sufficient amount of the hydrofluorocarbon polymermaterial is deposited on the top surface and sidewalls of the mask layer20 and the sidewalls and the bottom surface of the trench 11′. In anon-limiting illustrative example, the thicknesses of thehydrofluorocarbon polymer material at various portions of ahydrofluorocarbon polymer layer 30 can range from 200 nm to 2 microns.

The deposition rate and the thickness of the hydrofluorocarbon polymermaterial at various locations at the surfaces of the trench 11 and themask layer 20 at the end of each deposition step, which is includedamong the repetitive processing sequence between the processing step ofFIG. 1B and the processing step of FIG. 1G, can be calculated bymeasuring the thicknesses of various corresponding portions of thehydrofluorocarbon polymer layer 30 in the exemplary test structure ofFIG. 3.

Specifically, the hydrofluorocarbon polymer layer 30 in the exemplarytest structure of FIG. 3 includes a first hydrofluorocarbon polymerportion 30A having a bottom polymer thickness tp_b′. The firsthydrofluorocarbon polymer portion 30A of FIG. 3 corresponds to theportion of the hydrofluorocarbon polymer layer 30 located at a bottom ofthe trench 11 and having bottom polymer thickness tp_b in the exemplarystructure of FIG. 1C, and also corresponds the first hydrofluorocarbonpolymer portion 30A deposited on the bottom surface of the trench 11 inthe structures of FIG. 1F and any intermediate structure before theprocessing step of FIG. 1G immediate after a deposition step. Thehydrofluorocarbon polymer layer 30 in the exemplary test structure ofFIG. 3 further includes a second hydrofluorocarbon polymer portion 30Bhaving a sidewall polymer thickness tp_s′. The second hydrofluorocarbonpolymer portion 30B of FIG. 3 corresponds to the portion of thehydrofluorocarbon polymer layer 30 located at sidewalls of the trench 11and the mask layer 20 and having sidewall polymer thickness tp_s in theexemplary structure of FIG. 1C, and also corresponds the secondhydrofluorocarbon polymer portion 30B deposited on the sidewalls of thetrench 11 and the mask layer 20 in the structures of FIG. 1F and anyintermediate structure before the processing step of FIG. 1G immediateafter a deposition step. In addition, the hydrofluorocarbon polymerlayer 30 in the exemplary test structure of FIG. 3 includes a thirdhydrofluorocarbon polymer portion 30A having a top polymer thicknesstp_p′. The third hydrofluorocarbon polymer portion 30C of FIG. 3corresponds to the portion of the hydrofluorocarbon polymer layer 30located at the top surface of the mask layer 20 and having top polymerthickness tp_t in the exemplary structure of FIG. 1C, and alsocorresponds the third hydrofluorocarbon polymer portion 30C deposited onthe top surface of the mask layer 20 in the structures of FIG. 1F andany intermediate structure before the processing step of FIG. 1Gimmediate after a deposition step.

Since the various thicknesses of the hydrofluorocarbon polymer layer 30in the exemplary structures of FIGS. 1C and 1F and the exemplary teststructure of FIG. 3 are linearly proportional to the time duration ofthe deposition time used for depositing the hydrofluorocarbon polymerlayer 30, the deposition rates at the various portions of thehydrofluorocarbon polymer layer 30 in the exemplary structures of FIGS.1C and 1F and any intermediate structure before the processing step ofFIG. 1G immediate after a deposition step can be determined by measuringthe thicknesses of the various portions of the hydrofluorocarbon polymerlayer 30 in the exemplary test structure of FIG. 3.

EXAMPLES

Non-limiting examples of specific embodiments of the present disclosureare illustrated below, which demonstrate advantages of selectedembodiments of the present disclosure. The non-limiting examples are forillustrative purposes only, and do not limit the scope of the presentdisclosure by any means.

Referring to FIG. 4, the deposition rates of the hydrofluorocarbonpolymer material at various portions of the hydrofluorocarbon polymerlayer 30 is plotted for the case in which the fluorocarbon gas employedto generate the plasma during the deposition step is C₅HF₇ gas. In thisexample, the plasma pressure was 25 mTorr, the depth of the trench 11′was 120 microns, and the width of the trench 11′ was 70 microns. Theflow rate of the C₅HF₇ gas was 150 sccm, and the temperature of theprocess chamber was 20 degrees Celsius. In the graph, the horizontalaxis indicates the RF power coupled to the plasma in Watts.

In the graph of FIG. 4, the deposition rates for the firsthydrofluorocarbon polymer portion 30A of FIG. 3 are indicated by a curvelabeled “Bottom,” the deposition rates for the second hydrofluorocarbonpolymer portion 30B in FIG. 3 are indicated by a curve labeled “Side,”and the deposition rates for the third hydrofluorocarbon polymer portion30C in FIG. 3 are indicated by a curve labeled “Top.” It is noted thatthe deposition rates for the first hydrofluorocarbon polymer portion 30Aof FIG. 3 are substantially the same as the deposition rates for thefirst hydrofluorocarbon polymer portion 30A of FIG. 1F under the samedeposition condition, the deposition rates for the secondhydrofluorocarbon polymer portion 30B in FIG. 3 are substantially thesame as the deposition rates for the second hydrofluorocarbon polymerportion 30B of FIG. 1F under the same deposition condition, and thedeposition rates for the third hydrofluorocarbon polymer portion 30C inFIG. 3 are substantially the same as the deposition rates for the thirdhydrofluorocarbon polymer portion 30C of FIG. 1F under the samedeposition condition.

At 500 Watts RF source power and 1,800 Watts RF source power, the firstdeposition rate (represented by the curve labeled “Bottom”) is less thanthe second deposition rate (represented by the curve labeled “Side”),which is less than the third deposition rate (represented by the curvelabeled “Top”). This is typical of plasma deposition processes, whichproduce polymers within the plasma. Thus, the farther away a surface isfrom the ions of the plasma, the lesser the amount of deposition.

Referring to FIG. 5, deposition rates for a fluorocarbon polymer thatdoes not include hydrogen is illustrate for a comparative exemplarydeposition process employing C₄F₈ gas as a deposition gas. Thedeposition rates were measured on a sample having a configuration of theexemplary test structure of FIG. 3, The deposition rate of thefluorocarbon polymer from the comparative exemplary deposition processis the greatest at the top surface of the mask layer 20 as indicated bythe curve labeled “Top,” which is above curves labeled “Bottom” and“Side” and representing the deposition rates of the fluorocarbon polymerat the bottom surface of the trench and at the sidewalls of the trench,respectively. Further, before the deposition rate at the sidewall of thetrench increases to about 90% of the deposition rate at the top surfaceof the mask layer with the increase in the RF source power, thedeposition rate at the bottom of the trench reaches 50% of thedeposition rate at the top surface of the mask layer.

Referring back to FIG. 4, at 1,000 Watts RF source power, the depositionrate of the hydrofluorocarbon polymer at sidewalls of the trench 11′ isgreater than the deposition rate of the hydrofluorocarbon polymer on thetop surface of the mask layer 20 in the test structure of FIG. 3. Thephenomenon of a greater deposition rate of the hydrofluorocarbon polymermaterial at sidewalls of a trench than the deposition rate of thehydrofluorocarbon polymer material at the top surface of the mask layer20 is herein referred to as “superconformity.”

The inversion of the ratio of the deposition rate at the sidewalls ofthe trench 11′ to the deposition rate at the top surface of the masklayer 20 from typical values less than 1.0 to a value greater than 1.0is believed to be caused by differences in the deposition conditions,and in the resulting composition of the hydrofluorocarbon polymers,between the sidewalls of the trench 11′ and the top surface of the masklayer 20. At the top surface of the mask layer 20 and at the bottomsurface of the trench (11 or 11′), the direct current (DC) bias voltagebetween the lower electrode and the upper electrode plays a role inaccelerating the ions of the plasma toward the horizontal surfaces ofthe top surface of the mask layer 20 and at the bottom surface of thetrench (11 or 11′). At the sidewalls of the trench (11 or 11′) and themask layer 20, the DC bias voltage between the lower electrode and theupper electrode does not accelerate the ions of the plasma toward thesidewalls because of the direction of the DC electrical field issubstantially parallel to the predominant direction of the velocity ofthe ions. Thus, the average kinetic energy of hydrofluorocarbon ions andhydrofluorocarbon polymers impinging on the top surface of the masklayer 20 and at the bottom surface of the trench (11 or 11′) is greaterthan the average kinetic energy of hydrofluorocarbon ions andhydrofluorocarbon polymers impinging on the sidewalls of the trench (11or 11′) and the mask layer 20. Further, because the distance from theplasma is different between the top surface of the mask layer 20 and thebottom surface of the trench (11 or 11′), the deposition rates of thehydrofluorocarbon polymer material are different between the top surfaceof the mask layer 20 and the bottom surface of the trench (11 or 11′).

In one embodiment, the deposition conditions during each depositionprocess in a repeated sequence of alternating deposition processes andetch processes can achieve the condition of superconfirmity or acondition close to superconformity as illustrated in the 1,000 Watts RFsource power setting in FIG. 4. In this embodiment, thehydrofluorocarbon polymer layer 30 of FIGS. 1C, 1F, and 3 can include afirst hydrofluorocarbon polymer portion 30A deposited at a firstdeposition rate on the bottom surface of a trench (11 or 11′), a secondhydrofluorocarbon polymer portion 30B deposited at a second depositionrate on the sidewalls of the trench (11 or 11′), and a thirdhydrofluorocarbon polymer portion 30C deposited at a third depositionrate on a horizontal surface of the mask layer 20. The second depositionrate is at least 90% of the third deposition rate, and the firstdeposition rate is less than 50% of the third deposition rate. In somecases, the second deposition rate is greater than the third depositionrate. It is noted that the comparative exemplary deposition processillustrated in FIG. 5, which deposits a fluorocarbon polymer that doesnot include hydrogen, cannot simultaneous provide a deposition rate at asidewall of a trench that is at least 90% of the deposition rate at thetop surface of a mask layer without increasing the deposition rate atthe bottom of a trench to a level greater then 50% of the depositionrate at the top surface of the mask layer. In one embodiment, the seconddeposition rate is greater than the third deposition rate in thestructures of FIGS. 1C, 1F, and 3. Generally intramolecure hydrogen atomin fluorocarbon strengthen carbon-carbon bond which enable to reduce theprobability of much dissociation of fluorocarbon in a plasma. Thereforehydrofluorocarbon C_(x)H_(y)F_(z), wherein x is an integer not less than3 as defined above can provide large size species such as C2 and/or C3multiple carbon species more than C1 mono carbon species in a plasma. Alarge size species generally have higher sticking coefficient onsemiconductor material than monocarbon species, therefore thehydrofluorocarbon C_(x)H_(y)F_(z), wherein x is an integer not less than3, and y and z are positive integers not greater than 15, can producehigher deposition rate on sidewall than on bottom.

FIGS. 6A-6C illustrate optical emission spectra of three comparativeexemplary deposition processes that deposit a fluorocarbon polymer thatdoes not include hydrogen for comparative purposes. FIGS. 6D-6Fillustrate optical emission spectra for three deposition processes thatdeposit a hydrofluorocarbon polymer material according to embodiments ofthe present disclosure.

Specifically, FIG. 6A is an optical emission spectrum from the plasmagenerated in “Process 1,” which employed C₄F₈ as a deposition gas and aplasma was generated at 25 mTorr employing 1,800 Watts of RF sourcepower and 80 Watts of bias power at 20 degrees Celsius. FIG. 6B is anoptical emission spectrum from the plasma generated in “Process 2,”which employed C₄F₈ as a deposition gas and a plasma was generated at 25mTorr employing 1,000 Watts of RF source power and 80 Watts of biaspower at 20 degrees Celsius. FIG. 6C is an optical emission spectrumfrom the plasma generated in “Process 3,” which employed C₄F₈ as adeposition gas and a plasma was generated at 25 mTorr employing 500Watts of RF source power and 80 Watts of bias power at 20 degreesCelsius.

FIG. 6D is an optical emission spectrum from the plasma generated in“Process 4,” which employed C₅HF₇ as a deposition gas and a plasma wasgenerated at 25 mTorr employing 1,800 Watts of RF source power and 80Watts of bias power at 20 degrees Celsius. FIG. 6E is an opticalemission spectrum from the plasma generated in “Process 5,” whichemployed C₅HF₇ as a deposition gas and a plasma was generated at 25mTorr employing 1,000 Watts of RF source power and 80 Watts of biaspower at 20 degrees Celsius. FIG. 6F is an optical emission spectrumfrom the plasma generated in “Process 6,” which employed C₅HF₇ as adeposition gas and a plasma was generated at 25 mTorr employing 500Watts of RF source power and 80 Watts of bias power at 20 degreesCelsius.

The horizontal axes of the spectra represent the wavelength of theemitted light from the plasma, and the vertical axes of the spectrarepresent the intensity of the emitted light in arbitrary units (a.u.).The locations of emission peaks corresponding to emission from C₂, C₃,and CF₂ species are marked with dotted lines, which are located at about516 nm, about 412 nm, and about 263 nm. As used herein, “about” refersto a range of values within measurement error of instrumentation.

C₄F₈ plasmas under the condition of the RF source power in a range from500 Watts to 1,800 Watts produce predominantly CF₂ or CF₃ species. C₅HF₇gas under the condition of the RF source power in a range from 500 Wattsto 1,800 Watts, and in general, a hydrofluorocarbon gas having achemical formula of C_(x)H_(y)F_(z), wherein x is an integer selectedfrom 3, 4, 5, 6, and 7, y and z are positive integers not greater than15, under a suitable RF source power has a drastically differentdissociation pathway in the plasma, and hydrofluorocarbon species andmore complex fluorocarbon species.

In one embodiment, a plasma of the hydrofluorocarbon gas can begenerated at a condition that provides an optical emission spectrumincluding a C₃ peak at about 412 nm having a peak height that is twiceas high as a peak height of a CF₂ peak at about 263 nm during eachdeposition step among the repeated alternating sequence of the etchsteps and deposition steps as illustrated in FIGS. 6D and 6E.

In another embodiment, a plasma of the hydrofluorocarbon gas can begenerated at a condition that provides an optical emission spectrumincluding a highest peak that is one of a C₃ peak at about 412 nm or aC₂ peak at about 516 nm during each deposition step among the repeatedalternating sequence of the etch steps and deposition steps asillustrated in FIGS. 6D and 6E.

The repeated alternating sequence of the etch steps and deposition stepsemploying a hydrofluorocarbon gas having a chemical formula ofC_(x)H_(y)F_(z), wherein x is an integer selected from 3, 4, 5, 6, and7, y and z are positive integers not greater than 15, can provide a netetch rate that is comparable with net etch rates of a comparativeexemplary repeated alternating sequence of etch steps and depositionsteps employing a fluorocarbon gas such as C₄F₈. At the same time, therepeated alternating sequence of the etch steps and deposition stepsemploying the hydrofluorocarbon gas can provide a lesser undercutdimension u (See FIG. 1G) than undercut dimensions provided by thecomparative exemplary repeated alternating sequence.

FIG. 7 is a graph comparing net etch rates of various comparativeexemplary repetitive alternating sequences of etch processes anddeposition processes, and repetitive alternating sequences of etchprocesses and deposition processes according to various embodiments ofthe present disclosure. FIG. 8 is a graph comparing the undercutdimension of the various comparative exemplary repetitive alternatingsequences of etch processes and deposition processes, and the repetitivealternating sequences of etch processes and deposition processesaccording to various embodiments of the present disclosure.

Specifically, 3 micron wide lines were patterned in mask layers formedover a silicon substrate in each of the five samples employed togenerate the data in FIGS. 7 and 8. “Process A” was performed on a firstsample, “Process B” was performed on a second sample, “Process C” wasperformed on a third sample, “Process D” was performed on a fourthsample, and “Process E” was performed on the fifth sample. Process Aemployed a first comparative exemplary repetitive alternating sequencesof etch processes and deposition processes in which C₄F₈ was employed asthe deposition gas at a flow rate of 150 sccm, RF source power of 1,000Watts and bias power of 80 Watts were applied to the plasma at apressure of 25 mTorr, and the plasma was generated in a process chambermaintained at 20 degrees Celsius. Process B employed a secondcomparative exemplary repetitive alternating sequences of etch processesand deposition processes in which C₄F₈ was employed as the depositiongas at a flow rate of 150 sccm, RF source power of 1,000 Watts and biaspower of 80 Watts were applied to the plasma at a pressure of 25 mTorr,and the plasma was generated in a process chamber maintained at −10degrees Celsius.

Process C employed a first exemplary repetitive alternating sequences ofetch processes and deposition processes in which C₅HF₇ was employed asthe deposition gas at a flow rate of 150 sccm, RF source power of 1,800Watts and bias power of 80 Watts were applied to the plasma at apressure of 25 mTorr, and the plasma was generated in a process chambermaintained at 20 degrees Celsius. Process D employed a second exemplaryrepetitive alternating sequences of etch processes and depositionprocesses in which C₅HF₇ was employed as the deposition gas at a flowrate of 150 sccm, RF source power of 1,800 Watts and bias power of 80Watts were applied to the plasma at a pressure of 25 mTorr, and theplasma was generated in a process chamber maintained at −10 degreesCelsius. Process E employed a third exemplary repetitive alternatingsequences of etch processes and deposition processes in which C₅HF₇ wasemployed as the deposition gas at a flow rate of 150 sccm, RF sourcepower of 1,000 Watts and bias power of 80 Watts were applied to theplasma at a pressure of 25 mTorr, and the plasma was generated in aprocess chamber maintained at 20 degrees Celsius. Sulfur hexafluoridewas employed as the etchant gas across Processes A, B, C, D, and E.

Process A provided a net etch rate of about 4.6 microns per minute andan undercut dimension u (see FIG. 1G) of about 520 nm for a 3 micronwide line trench. Process A did not produce a micromasking phenomenonwithin the line trench, and provided minimal sidewall roughness andbottom roughness.

Process B provided a net etch rate of about 4.3 microns per minute andan undercut dimension u of about 150 nm for a 3 micron wide line trench.However, Process B produced a micromasking phenomenon in the linetrench, thereby generating significant sidewall roughness and bottomroughness, and rendering the line trench unusable for formation of athrough substrate via structure.

Process C provided a net etch rate of about 4.2 microns per minute andan under dimension u of about 550 nm for a 3 micron wide line trench.Process C did not produce a micromasking phenomenon within the linetrench, and provided minimal sidewall roughness and bottom roughness.

Process D provided a net etch rate of about 4.1 microns per minute andan under dimension u of about 490 nm for a 3 micron wide line trench.Process D did not produce a micromasking phenomenon within the linetrench, and provided minimal sidewall roughness and bottom roughness.

Process E provided a net etch rate of about 5.1 microns per minute andan under dimension u of about 325 nm for a 3 micron wide line trench.Process D did not produce a micromasking phenomenon within the linetrench, and provided minimal sidewall roughness and bottom roughness.

Thus, processes of the present disclosure, such as Process E, can beemployed to form a deep trench in a semiconductor substrate at a highnet etch rate without micromasking and providing a small undercutdimension, which can be, for example, less than 350 nm for a 3 micronwide trench. For example, compared to Process A, Process E provide agreater etch rate and a reduce undercut by at least 30%.

The presence of hydrogen in the hydrofluorocarbon polymer material inthe hydrofluorocarbon polymer layer 30 in FIGS. 1C, 1F, and 3 enhancesresistance of the hydrofluorocarbon polymer material to afluorine-containing etchant gas, such as sulfur hexafluoride, overfluorocarbon polymers that do not include hydrogen. FIGS. 9 and 10compare etch resistance to exposure to sulfur hexafluoride plasma ofhydrofluorocarbon polymers according to embodiments of the presentdisclosure with corresponding etch resistance of fluorocarbon polymersgenerated from comparative exemplary deposition processes.

Specifically, in Process P, a first sample was generated by depositing afluorocarbon polymer layer from a C₄F₈ plasma on a planar substrate. Theplasma was generated with 1,000 Watts of RF source power and 80 Watts ofbias power, at a pressure of 25 mTorr and with 150 sccm of C₄F₈ flow,and at a temperature of 20 degrees Celsius. The thickness of thefluorocarbon polymer layer of the first sample was measured prior toexposure to a plasma of sulfur hexafluoride, and after various timedurations of exposure to the plasma of sulfur hexafluoride thatsimulates an etch process for silicon. The initial thickness of thefluorocarbon polymer layer in the first sample was 387 nm. Theproperties of the fluorocarbon polymer material of the first samplerepresents the properties of the fluorocarbon polymer of Process Adescribed above as formed on a top surface of a mask layer and a bottomsurface of a trench in a structure having the same configuration as theexemplary test structure of FIG. 3 because polymers formed on horizontalsurfaces of a substrate are subject to the full impact of the bias powerapplied to the plasma.

In Process P, a second sample was generated by depositing ahydrofluorocarbon polymer layer from a C₅HF₇ plasma on a planarsubstrate according to an embodiment of the present disclosure. Theplasma was generated with 1,000 Watts of RF source power and 80 Watts ofbias power, at a pressure of 25 mTorr and with 150 sccm of C₅HF₇ flow,and at a temperature of 20 degrees Celsius. The thickness of thehydrofluorocarbon polymer layer in the second sample was measured priorto exposure to a plasma of sulfur hexafluoride, and after various timedurations of exposure to the plasma of sulfur hexafluoride thatsimulates an etch process for silicon. The initial thickness of thehydrofluorocarbon polymer layer in the second sample was 549 nm. Theproperties of the hydrofluorocarbon polymer material of the secondsample represents the properties of the hydrofluorocarbon polymer ofProcess E described above as formed on the top surface of a mask layer20 and the bottom surface of the trench (11 or 11′) in the exemplarystructure of FIGS. 1C and 1F and in the exemplary test structure of FIG.3 because polymers formed on horizontal surfaces of a substrate aresubject to the full impact of the bias power applied to the plasma.

In Process R, a third sample was generated by depositing a fluorocarbonpolymer layer from a C₄F₈ plasma on a planar substrate. The plasma wasgenerated with 1,000 Watts of RF source power and without any biaspower, at a pressure of 25 mTorr and with 150 sccm of C₄F₈ flow, and ata temperature of 20 degrees Celsius. The thickness of the fluorocarbonlayer in the third sample was measured prior to exposure to a plasma ofsulfur hexafluoride, and after various time durations of exposure to theplasma of sulfur hexafluoride that simulates an etch process forsilicon. The initial thickness of the fluorocarbon polymer layer in thethird sample was 674 nm. The properties of the fluorocarbon polymermaterial of the third sample represents the properties of thefluorocarbon polymer of Process A described above as formed on sidewallsof a mask layer and sidewalls of a trench in a structure having the sameconfiguration as the exemplary test structure of FIG. 3 because polymersformed on vertical surfaces of a substrate are not significantlyaffected by the bias power applied to the plasma.

In Process S, a fourth sample was generated by depositing ahydrofluorocarbon polymer layer from a C₅HF₇ plasma on a planarsubstrate according to an embodiment of the present disclosure. Theplasma was generated with 1,000 Watts of RF source power and without anybias power, at a pressure of 25 mTorr and with 150 sccm of C₅HF₇ flow,and at a temperature of 20 degrees Celsius. The thickness of thehydrofluorocarbon polymer layer of the fourth sample was measured priorto exposure to a plasma of sulfur hexafluoride, and after various timedurations of exposure to the plasma of sulfur hexafluoride thatsimulates an etch process for silicon. The initial thickness of thehydrofluorocarbon polymer layer in the fourth sample was 520 nm. Theproperties of the hydrofluorocarbon polymer material of the fourthsample represents the properties of the hydrofluorocarbon polymer ofProcess E described above as formed on the sidewalls of the mask layer20 and the sidewalls of the trench (11 or 11′) in the exemplarystructure of FIGS. 1C and 1F and in the exemplary test structure of FIG.3 because polymers formed on vertical surfaces of a substrate are notsignificantly affected by the bias power applied to the plasma.

The thicknesses of remaining polymers as a percentage of the initialthickness are plotted in FIGS. 9 and 10 for Processes P, Q, R, and S.Comparison of the various curves of FIGS. 9 and 10 show that thehydrofluorocarbon polymers derived from a C₅HF₇ plasma is more etchresistant than fluorocarbon polymers derived from a C₄F₈ plasma undersame conditions. Thus, presence of hydrogen in the hydrofluorocarbonpolymer material provides more protection to the sidewalls of the trenchduring etching, and contributes to the superior performance of Process Erelative to Process A as illustrated in FIGS. 7 and 8.

Further, FIGS. 9 and 10 clearly illustrate that there is a compositionaldifference between the hydrofluorocarbon polymer material deposited onthe top surface of the mask layer 20 and the bottom surface of thetrench (11 or 11′) in the exemplary structure of FIGS. 1C and 1F and theexemplary test structure of FIG. 3 relative to the hydrofluorocarbonpolymer material deposited on the sidewalls of the mask layer 20 and thesidewalls of the trench (11 or 11′) in the exemplary structure of FIGS.1C and 1F and the exemplary test structure of FIG. 3. Specifically,Process S shows more etch resistance to sulfur hexafluoride etch thanProcess Q. Thus, the hydrofluorocarbon polymer material deposited on thesidewalls of the mask layer 20 and the sidewalls of the trench (11 or11′) in the exemplary structure of FIGS. 1C and 1F and the exemplarytest structure of FIG. 3 is more etch resistant than thehydrofluorocarbon polymer material deposited on the top surface of themask layer 20 and the bottom surface of the trench (11 or 11′) in theexemplary structure of FIGS. 1C and 1F and the exemplary test structureof FIG. 3.

Referring back to FIGS. 1A-1L and 3, the composition of various portionsof a hydrofluorocarbon polymer layer 30 at the end of each depositionstep, which is included among the repetitive processing sequence betweenthe processing step of FIG. 1B and the processing step of FIG. 1G, isthe same as the composition of the corresponding portions of thehydrofluorocarbon polymer layer 30 within the exemplary test structureof FIG. 3. By selecting a deposition process such as Process E for thedeposition steps of the repetitive processing sequence of FIGS. 1B-1G,the various portions of the hydrofluorocarbon polymer layer 30 can havedifferent compositions.

For example, the first hydrofluorocarbon polymer portion 30A depositedon the bottom surface of the trench 11 in the structures of FIG. 1F andany intermediate structure before the processing step of FIG. 1Gimmediate after a deposition step can have the same composition as thehydrofluorocarbon polymer material in the second sample prior toexposure to SF₆. The second hydrofluorocarbon polymer portion 30Bdeposited on the sidewalls of the trench 11 and the mask layer 20 in thestructures of FIG. 1F and any intermediate structure before theprocessing step of FIG. 1G immediate after a deposition step can havethe same composition as the hydrofluorocarbon polymer material in thefourth sample prior to exposure to SF₆. In addition, the thirdhydrofluorocarbon polymer portion 30C deposited on the top surface ofthe mask layer 20 in the structures of FIG. 1F and any intermediatestructure before the processing step of FIG. 1G immediate after adeposition step can have the same composition as the hydrofluorocarbonpolymer material in the second sample prior to exposure to SF₆.

In addition, the first hydrofluorocarbon polymer portion 30A depositedon the bottom surface of the trench 11 in the structures of FIG. 1F andany intermediate structure before the processing step of FIG. 1Gimmediate after a deposition step can have the same etch resistance to afluorine-containing etchant gas as the second sample (which ischaracterized by the curve labeled “Process Q”). The secondhydrofluorocarbon polymer portion 30B deposited on the sidewalls of thetrench 11 and the mask layer 20 in the structures of FIG. 1F and anyintermediate structure before the processing step of FIG. 1G immediateafter a deposition step can have the same etch resistance to afluorine-containing etchant gas as the fourth sample (which ischaracterized by the curve labeled “Process S”). In addition, the thirdhydrofluorocarbon polymer portion 30C deposited on the top surface ofthe mask layer 20 in the structures of FIG. 1F and any intermediatestructure before the processing step of FIG. 1G immediate after adeposition step can have the same etch resistance to afluorine-containing etchant gas as the second sample (which ischaracterized by the curve labeled “Process Q”).

Thus, the first composition of the first hydrofluorocarbon polymerportion 30A in the hydrofluorocarbon polymer layer 30 of FIGS. 1C, 1F,and 3 can be the same as the composition of the hydrofluorocarbonpolymer material in the second sample, the second composition of thesecond hydrofluorocarbon polymer portion 30B in the hydrofluorocarbonpolymer layer of FIGS. 1C, 1F, and 3 can be the same as the compositionof the hydrofluorocarbon polymer material in the fourth sample, and thethird composition of the third hydrofluorocarbon polymer portion 30C inthe hydrofluorocarbon polymer layer 30 of FIGS. 1C, 1F, and 3 can be thesame as the composition of the hydrofluorocarbon polymer material in thesecond sample. The first composition is different from the secondcomposition. The second composition can be more etch resistant to anetchant gas employed during the etch process than the first composition.The etch process of the repetitive alternating sequence can etch a firstportion of the hydrofluorocarbon polymer located at the bottom surfaceof a trench (11, 11′), i.e., the first hydrofluorocarbon polymer portion30A, at a faster rate than a second portion of the hydrofluorocarbonpolymer located at the sidewalls of the trench (11, 11′), i.e., thesecond hydrofluorocarbon polymer portion 30B.

Referring to FIG. 11, X-ray photoemission spectroscopy was employed tomeasure the atomic ratio of fluorine to carbon on the first, second,third, and fourth samples before, and after exposure to sulfurhexafluoride plasma at 25 mTorr for several times up to and including 5minutes at 1800 Watts. As discussed above, the first sample wassubjected to Process P, which is a first comparative process. The secondsample was subjected to Process Q, which includes a first exemplarydeposition process according to the present disclosure. The third samplewas subjected to Process R, which is a second comparative process. Thefourth sample was subjected to Process S, which includes a secondexemplary deposition process according to the present disclosure

While the atomic ratio of fluorine to carbon changes by less than 0.2for the first sample and the third sample that include fluorocarbonpolymers (that do not include hydrogen), the atomic ratio of fluorine tocarbon changed by about 0.5˜0.6 for the third sample and the fourthsample that include hydrofluorocarbon polymers. Fluorine atoms replacehydrogen atoms during the treatment with the sulfur hexafluoride plasma.Thus, when an etch process is performed during the repetitivealternating sequences of the etch processes and deposition processes ofFIGS. 1B-1G, a plasma of a fluorine-containing etchant can causesubstitution of a significant fraction of hydrogen atoms in thehydrofluorocarbon polymer material with fluorine atoms before thehydrofluorocarbon polymer material becomes rich in fluorine, andeventually removed from the sidewalls of the trench 11 and the masklayer 20.

The change in the fluorine to carbon atomic ratio represents a minimumin the hydrogen content in the hydrofluorocarbon polymer material.Significant differences have been observed in the hydrogen compositionin the hydrofluorocarbon polymer materials generated by the methods ofthe present disclosure. In general, the hydrofluorocarbon polymermaterial in the hydrofluorocarbon polymer layer 30 of FIGS. 1C, 1F, and3 can includes carbon at an atomic concentration in a range from 20% to50%, hydrogen at an atomic concentration from 4% to 70%, and fluorine atan atomic concentration from 4% to 70%.

In one embodiment, the first composition of the first hydrofluorocarbonpolymer portion 30A in the hydrofluorocarbon polymer layer 30 of FIGS.1C, 1F, and 3 includes hydrogen at a first hydrogen atomic percentage,and the second composition of the second hydrofluorocarbon polymerportion 30B in the hydrofluorocarbon polymer layer 30 of FIGS. 1C, 1F,and 3 includes hydrogen at a second hydrogen atomic percentage that isgreater than the first hydrogen atomic percentage. In one embodiment,the second hydrogen atomic percentage is greater than the first hydrogenatomic percentage by at least 5%. In another embodiment, the secondhydrogen atomic percentage is greater than the first hydrogen atomicpercentage by at least 10%. In yet another embodiment, the secondhydrogen atomic percentage is greater than the first hydrogen atomicpercentage by at least 15%.

Further, in one embodiment, the ratio of fluorine to hydrogen can beless than 15 within the hydrofluorocarbon polymer as illustrated in FIG.11. (See Pre-SF₆ treatment data for Process Q and Process S.)

Referring to FIGS. 12, 13, 14, and 15, Fourier-transformation infrared(FTIR) spectroscopy spectra are shown from the hydrofluorocarbon polymerdeposits in the first, second, third, and fourth samples, respectively,as measured before, and after, treatment with SF₆ plasma. FIG. 12 showsa pre-treatment FTIR spectrum 1210 and a post-treatment FTIR spectrum1220 for the first sample that is subjected to Process P describedabove. FIG. 13 shows a pre-treatment FTIR spectrum 1310 and apost-treatment FTIR spectrum 1320 for the second sample that issubjected to Process Q described above. FIG. 14 shows a pre-treatmentFTIR spectrum 1410 and a post-treatment FTIR spectrum 1420 for the thirdsample that is subjected to Process R described above. FIG. 15 shows apre-treatment FTIR spectrum 1510 and a post-treatment FTIR spectrum 1520for the fourth sample that is subjected to Process S described above.

Significant amounts of C—H bonds, represented by a broad peak in thewavenumber range between 2000⁻¹ to 3000 cm⁻¹ in the pre-treatment FTIRspectrum 1510, is observed for the fourth sample. The broad peakdisappears after the SF₆ treatment as illustrated in the post-treatmentFTIR spectrum 1520. However, a corresponding peak is not discernable inthe pre-treatment FTIR spectrum 1310 or the post-treatment FTIR spectrum1320 of the second sample. Typical fluorocarbon absorbance peaks such asa peak at 1240 cm⁻¹, caused by CF, CF₂, and CF₃, decrease after the SF₆treatment in the second sample and in the fourth sample.

Referring to FIGS. 16, 17, 18, and 19, normalized absorbance of thehydrofluorocarbon polymer deposits in the first, second, third, andfourth sample, respectively, are shown before, and after, treatment withSF₆ plasma for various peaks representing various chemical bonds. FIGS.16 and 18 show normalized absorbance of the peaks at 1112 cm⁻¹, 1240cm⁻¹, 618 cm⁻¹, and 1721 cm⁻¹. FIGS. 17 and 19 show normalizedabsorbance of the peaks at 1112 cm⁻¹, 1240 cm⁻¹, 618 cm⁻¹, 1721 cm⁻¹,and 2960 cm⁻¹. The peak at 2960 cm⁻¹ corresponds to CH_(x) bonds (inwhich x is a positive integer) in the hydrofluorocarbon polymer materialin the second and fourth samples. While the height of the peak at 2960cm⁻¹ is at about 0.05 in the second sample before and after thetreatment with SF₆ (See FIG. 17), the height of the peak at 2960 cm⁻¹ isabout 0.57 in the fourth sample before the treatment with SF₆ (See FIG.19). This peak in the fourth sample decreases to about 0.07 after thetreatment with SF₆, which represents replacement of CH_(x) bonds withCF_(x) bonds.

The difference in the height of the peak at 2960 cm⁻¹ between the secondsample and the fourth sample prior to the treatment with SF₆ correspondsto the differences between the atomic concentration of hydrogen in thefirst composition and the atomic concentration of hydrogen in the secondcomposition, i.e., the composition of the first hydrofluorocarbonpolymer portion 30A and the composition of the second hydrofluorocarbonpolymer portion 30B in FIGS. 1C, 1F, and 3. The high concentration ofhydrogen atoms in the second hydrofluorocarbon polymer portion 30B iscaused by a higher rate of hydrogen incorporation when thehydrofluorocarbon polymer is deposited with little ion energy, i.e.,without significant energy gained by the bias voltage applied across thelower electrode and the upper electrode in the process chamber. Thehydrogen rich film in the hydrofluorocarbon polymer portion 30B isreduced and incorporates fluorine upon exposure to SF₆, which changesfilm density and becoming less resistant to the SF₆ plasma.

Thus, a deposition process that employs a hydrofluorocarbon gas having achemical formula of C_(x)H_(y)F_(z), wherein x is an integer selectedfrom 3, 4, 5, 6, and 7, y and z are positive integers not greater than15 can be employed in a repetitive alternating sequence of etchprocesses and deposition processes to provide a deep trench in asemiconductor substrate such that the net etch rate is enhanced andundercut is reduced compared to comparative exemplary repetitivealternating sequence of etch processes and deposition processesemploying a fluorocarbon gas that does not include hydrogen as thedeposition gas.

While the present disclosure has been described employing a deep trenchas a feature, the methods of the present disclosure can be employed toform a structure including any feature that is etched within in asubstrate such as a shallow trench, a contact trench, a circular orannular via or contact feature, or any other trench having a recessedsurface relative to a top surface. Such variations are expresslycontemplated herein. Further, as used herein, a “trench” refers to anytype of cavity having a surface that is recessed into a substraterelative to another surface of the substrate.

While the disclosure has been described in terms of specificembodiments, it is evident in view of the foregoing description thatnumerous alternatives, modifications and variations will be apparent tothose skilled in the art. Accordingly, the disclosure is intended toencompass all such alternatives, modifications and variations which fallwithin the scope and spirit of the disclosure and the following claims.

What is claimed is:
 1. A semiconductor structure comprising: a stack ofa semiconductor substrate and a mask layer having an opening therein; atrench located within said semiconductor substrate and underlying saidopening and having a vertically modulated width; and a hydrofluorocarbonpolymer layer contiguously extending from a top surface and sidewalls ofsaid mask layer, through sidewalls of said trench, and to a bottomsurface of said trench, wherein said hydrofluorocarbon polymer layer hasa first composition at said bottom surface of said trench, saidhydrofluorocarbon polymer layer has a second composition at saidsidewalls of said trench, and said second composition is different fromsaid first composition, wherein said first composition includes hydrogenat first hydrogen atomic percentage, and said second compositionincludes hydrogen at a second hydrogen atomic percentage that is greaterthan said first hydrogen atomic percentage.
 2. The semiconductorstructure of claim 1, wherein said second hydrogen atomic percentage isgreater than said first hydrogen atomic percentage by at least 5%. 3.The semiconductor structure of claim 1, said hydrofluorocarbon polymerlayer includes carbon at an atomic concentration in a range from 20% to50%, hydrogen at an atomic concentration from 4% to 70%, and fluorine atan atomic concentration from 4% to 70%.
 4. The semiconductor structureof claim 1, wherein a ratio of fluorine to hydrogen is less than 15within an entirety of said hydrofluorocarbon polymer layer.
 5. Thesemiconductor structure of claim 1, wherein said hydrofluorocarbonpolymer layer includes a first hydrofluorocarbon polymer portion locatedon said bottom surface and having a first thickness, a secondhydrofluorocarbon polymer portion located on said sidewalls of saidtrench and having a second thickness, and a third hydrofluorocarbonpolymer portion located on a horizontal surface of said mask layer andhaving a third thickness, wherein said second thickness is at least 90%of said third thickness, and said first thickness is less than 50% ofsaid third thickness.
 6. The semiconductor structure of claim 1, whereinsaid hydrofluorocarbon polymer layer includes a first hydrofluorocarbonpolymer portion located on said bottom surface, and a secondhydrofluorocarbon polymer portion located on said sidewalls of saidtrench.
 7. The semiconductor structure of claim 6, wherein saidhydrofluorocarbon polymer layer further comprises a thirdhydrofluorocarbon polymer portion located on a horizontal surface ofsaid mask layer.
 8. The semiconductor structure of claim 7, wherein saidfirst hydrofluorocarbon polymer portion has a first thickness, saidsecond hydrofluorocarbon polymer portion has a second thickness, andsaid third hydrofluorocarbon polymer portion has a third thickness,wherein said second thickness is at least 90% of said third thickness,and said first thickness is less than 50% of said third thickness. 9.The semiconductor structure of claim 8, wherein said second thickness isgreater than said third thickness.
 10. The semiconductor structure ofclaim 9, wherein said mask layer includes a dielectric material selectedfrom doped silicon oxide, undoped silicon oxide, silicon nitride,silicon oxynitride, a dielectric metal oxide, or a combination thereof.11. The semiconductor structure of claim 1, wherein said trench has avertically modulated width that changes with a distance from said masklayer.
 12. The semiconductor structure of claim 11, wherein saidvertically modulated width gradually increases and gradually decreasesmultiple times with a monotonic change of said distance from said masklayer.
 13. The semiconductor structure of claim 11, wherein acombination of a gradual increase and a gradual decrease with amonotonic change of a distance from said mask layer repeats a number oftimes, said number being in a range from 2 to 1,000.
 14. Thesemiconductor structure of claim 1, wherein said semiconductor substrateincludes a silicon-containing semiconductor material.